Roasting pyrites



Nov. 27, 1956 J. R. WEST Erm. 2,772,153

RoAsTI'NG PYRITES 2 JAMES 2.

FREDE RIC/f GORMLE f NOV. 27, 1956 J, R, WEST ETAL ROASTING PYRITESFiled Aug. 4, -1955 2 lSheets-Sheet 2 ok Now (ONDNSEIZ u? Sv N2 E lPDEHEATER llal N HQ .POI

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United States Patent ROASTING FSZRLTES James R. West, Pittsburgh, Pa.,and Frederick Gormley, Vera Cruz, Mexico, assignors to Texas GulfSulphur Company, New York, N. Y., a corporation of Texas Application'August 4, 1955, Serial No. 526,460

7 Claims. (CL75- 9) This invention relates to the roasting of pyrites,and a major object is Yto provide a method of'roastmg 1t to produceelemental sulfur (S) and ferrie oxide (P ezOs):

Another object is to provide such a method 1n which inert gas 'is usedto 4free the labile sulfur as the iirst step, or stage, yof roastingwith production of a rmmrnal amount of sulfur dioxide (SO2).

Yet another object is to provide a method of the foregoing types inwhich roasting of the sulfur contained in pyrites is eifected chiey bymeans Vof sulfur dioxide.

As special object is to provide a method 1n accordance with theforegoing objects in which pyrrhotite (FeS) 1s reacted with sulfurdioxide to produce magnetite (Fe304) and elemental sulfur, and in whichthe sole source of sulfur dioxide is produced by reacting ferrie oxidewith pyrrhotite to producemagnetite and sulfur dioxide.

Still another object is to eect roasting of pyrites 1n accordance withthe foregoing objects to produce ferrie oxide containing less residualsulfur than has been the case with prior roasting methods.

A still further object is to effect roasting of pyrites in accordancewith the foregoing objects under fluidizing conditions.

The invention will be `described with reference to the accompanyingdrawings in which:

Fig. 1 is a schematic representation or" one mode of practicing theinvention;

Fig. 2 is a iiow sheet representing one embodiment of the invention aspracticed with uidization;

Fig. 3 is a flow sheet illustrating another embodiment of the inventionusing ui'dization; and

Fig. 4 is still another ow sheet representing yet another uidizedembodiment.

We have discovered, and it is upon this that the'invention is largelypredicated, vthat the stated objects of the invention are attained bytreating pyrites with an inert gas that is non-oxidizing to sulfur, andpreferably comprising essentially at least one member lofthe groupconsisting of nitrogen (N2) and sulfur dioxide at a temperature at whichthe labile sulfur atom is drivenfrom the pyrites with formation ofpyrrhotite, treating the resultant pyrrhotite with at least one memberof the group Vconsisting of oxygen (O2) and sulfur dioxide at atemperature to convert it to magnetite, vheating the magnetite with anoxygen-containing gas at a temperature'to convertit to ferrie oxide, andrecovering the sulfur produced and the Vferric oxide produced.

Having reference now to the drawings, Fig. 1 shows schematically areactor i inthe form of a vertical moving bed shaft furnace into theupper end of which, as indicated in the drawing, pyrites is introducedthrough suitable ,feeding mechanism, not shown. The pyrites may suitably2,772,153 aented Nov. =27, 1956 The pyrrhotite thus formed reacts, in`moving'downthe shaft, with sulfur dioxide toV producemagnetite-according to the following reaction Pyrrhotite likewise reactswith any oxygen remaining'in the upmoving gases in accordance with the,following The magnetite formed by either lor both ofRea'ctions 2 and 3then reacts with the oxygen of the air introduced into the bottom of thereactor, asshown, accordingtothe following reaction 4portion beingpassed at 4 to a stack. In the '.pra'c'tice'of this embodiment of theinvention the air suppli'edtothe reactor is controlled in an amount suchas to' eect Reaction 3 yand to avoid having any 'substantial excessofoxygenpassing into the upper portions'of the reactor, whereby oxidationof the vsulfur of the 'pyr'ites andpyrrhotite is avoided. `In this waythe maximum amount 'of sulfur is recovered as such.

Various modications of the embodiment of Fig'lof the invention arepermissible. For instance, thefern'c oxide from reactor 1 may be passed'to a chloridizing reactor into which common salt, air and fuel areintroduced for conversion of non-ferrous metals, such las nickel. and"copper, present in the ore into soluble chlorides. Similarly, the excesssulfur dioxide from condenser 2 that is-'not required for circulation inthe system maybe passed 'toa liquefaction plant to recover sulfurdioxide for Vdesired use. In this latter embodiment it Amaybe'preferable tto supply oxygen instead of air to the bottom-of shaftfurnace lfwhereby there is no necessity for separating nitrogen from thesulfur dioxide'that is to be liquefied.

In the preferred embodiment of the invention the various stages ofthe'process are carried out under uidizing conditions, as illustrated inFigs. 2 to 4. Referring lto Fig. 2, pyrites in a form adapted to beuidized is passed to a preheater 5 where it is uidized by a stream ofhot gas composed of nitrogen and sulfur dioxide from 'a heater 6, thetemperature of the gas being such as to drive the labile sulfur atomfrom the pyrites and form pyrrhotite in Jaccordance with Reaction 1. Thepyrrhotite passes into reactor 7 where it is uidized with a gas composedchiey of oxygen and nitrogen at a temperature such as to cause Reactions2 and 3 to occur. The resulting magnetite then passes to a reactor 8where it is fluidized with air "ata temperature to effect Reaction 4,with the olfg`as'(largely O2 and N2) being passed to reactor v7.

lyrites is fed likewise to a preheater 5a Where it *is uidlzed with hotgas from heater 6 with production of pyrrhotite according to Reaction 1.The pyrrhotite thus produced passes to a reactor 7a where it is uidizedwith the mixture of sulfur dioxide and nitrogen from reactor 7, land bysulfur dioxide from heater 6, with production of magnetite and elementalsulfur. The magnetitefrom reactors 7 and 7a is then passed to reactor`8, where it is fluidized by air and from which ferric oxide, perReaction 4, is withdrawn.

The mixture of sulfur dioxide, sulfur vapor and fuitrogen fromreactorsand Sa is passed-to a sulfurJcondenser 9 of any desired type from whichthe :sulfuris recovered, with the residual gas being passed to a stack`or Ato a sulfur dioxide liquetaction plant.

The mixture of sulfur dioxide, nitrogen and sulfur vapor from reactor 7ais likewise passed to sulfur condenser 9a for recovery of its content ofsulfur, the residual sulfur dioxide and nitrogen then being passed toheater 6Yfor recirculation inthe system in the manner described.

Although preheater 5, reactor 7 Yand reactor 8 are shown in the ow sheetas separate units, it will be understood that the three stages may becombined in a single uidized reactor with the top, middle and bottomzones being represented, respectively, by preheater 5, reactor 7 andreactor 8. Likewise, the same thing applies 'to preheater 5a and reactor7a.

If desired, all or a portion of the ferrie oxide from reactor 8 may bepassed to a chloridizing reactoril in Y the manner and for the purposedescribed in connection with Fig. 1.

Having reference now to Fig. 3,.here again pyrites of appropriate sizeis fed to aV preheater 11 where it is Y uidized with an inert gas fromgenerator 12 at a temperature sufficient to drive the labile sulfur atomfrom Ythe ore and form pyrrhotite. The inert gas supplied from generator12 may be flue gas composed largely of nitrogen and carbon dioxide, orit may be blast furnace gas, or other gas that is substantially freefrom oxygen and nonreactive with sulfur under the roasting conditions. Aportion of the pyrrhotite from preheater 11 then is uidized in a reactor13 with sulfur dioxide under conditions in accordance with Reaction 2,thus forming magnetite and elemental sulfur. Another portion of thepyrrhotite formed in preheater 11 is passed to a reactor 13a where it isuidizcd with sulfur dioxide at a temperature* to cause Reaction 2 toproceed, likewise with production of magnetitie and sulfur vapor. VThemagnetite from reactors 13 and 13a then passes to a reactor 14 where itis treated at a temperature such that with oxygen or a gas containing ahigh'percentage, say 85 to 95 percent, of oxygen, preferably in anamount such that the ott-gas, if any, is substantially oxygen-free andconsists essentially of nitrogen. Y

An important feature of this embodiment of the Yinvention is therecirculation, asY shown, of a portion of the ferrie oxide from reactor14 Vto reactor 13 where the following reaction occurs Reaction 5constitutes in this embodiment the sole source of the sulfur dioxideused in this embodiment, which is important and desirable in thatoxidation of sulfur in reactors 13 and 13a and preheater 11 is avoidedFerrie oxide from reactor 14 is withdrawn and passed Y to use orstorage, and the mixture of inert gas and sulfur vapor from preheater 11is passed to a suitable sulfur condenser 15 from which sulfur iswithdrawn, with the inert gas being wasted. Similarly, the mixture ofsulfur dioxiderand sulfur vapor from reactors 13 Vand 13a are v passedto a condenser 15a for recovery of the sulfur content, the sulfurdioxide from the condenser being passed to a heater 16 for recirculationto reactors 13 and 13a, as described.

As in the case of Fig. 2, the separate stages of pre- Vheater 11 andreactors 13 and V14 may be combined in a single fluidized unit. Y

The embodiment of Fig. 4 is generally similar to that kof Fig. 3 in thatpyrites of appropriate sizeA is iluidized Reaction 2. The magnetite fromthe two reactors is then Vfiuidized with air in a reactor 19 at atemperature to convert the magnetite Vto ferrie oxide in aodlle withReaction 4. In this embodiment the air is preferably supplied to reactor19 in such an amount that the product gas consists essentially ofnitrogen which is passed as the inert gas to preheater 17. Preferably, aportion of the ferric oxide leaving reactor 19 is recycled to reactor18, as shown, for the purpose described in connection with Fig. 3. Themixture of sulfur dioxide and sulfur vapor from reactors 18 and 18a ispassed to an appropriate condenser 21for recoveryV of the' sulfur, withthe separated sulfur dioxide passing to a heater 22 whence it is fed toreactors 18 and 18a. Here, also, preheater 17 and reactors 18 and 19 maybe combined in a single uidized unit.

Although in various embodiments two sulfur condensers have been shownand described, it will be understood that all of the sulfurvapor-carrying gases Vmay be treated in a single condenser. Likewise,'inall instances the ferric oxide may go to a chloridizer, per Figs. 1 and2.

According to the provisions Yof the patent statutes, We have explainedthe principle of our invention and have illustrated and described whatwe now consider to represent its best embodiment. However, we desire tohave it understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically illustratedand described.

We claim:

l. That method of roasting pyrites to produce sulfur and ferric oxidecomprising V'fluidizing one portion of pyrites with nitrogen-containinggas substantially free from oxygen at a temperature to drive off thelabile sulfur atom and form pyrrhotite, separately tuidizing a secondportion of pyrites in the same manner, recovering the sulfurY from saidtreatments, liuidizing the pyrrhotite from said one portion with anoxygen-containing gas at atemperature to convert it to magnetiteand'produce sulfur dioxide, uidizing the pyrrhotite from said secondportion with sulfur dioxide, including that from said one portion, at atemperature to convert the pyrrhotite to magnetite with production of amixture of sulfur dioxide and sulfur vapor, condensing sulfur from saidmixture and passing part of the residual sulfur dioxide to treat saidone portion and passing another part to treat the pyrrhotite from secondportion, uniting the magnetite thus produced and uidizing it with anoxygen-containing gas at a temperature to convert it to ferric oxide,and

pyrites with nitrogen-containing gas substantially freeV from oxygen atYa temperature to driveV ot the labile sulfur atom and form pyrrhotite,separately uidizing a second portion of pyrites in the same manner,recovering the sulfur from said treatments, uidizing the pyrrhotite fromsaid one portion with an oxygen-containing gas ata temperature toconvert it to magnetite and produce sulfur dioxide, treating thepyrrhotite from said second portion with sulfur dioxide, including thatfrom said one portion, at a temperature and with uidization to convertit to magnetite with production of a mixture of sulfur dioxide andsulfur vapor, condensing sulfur from said mixture and passing part ofthe residual sulfur dioxide to treat said one portion and passinganother part to treat the pyrrhotite from second portion, uniting themagnetite thus produced and fluidizing it with an oxygen-containing gasto convert it to ferric oxide, returning a portion of said ferrie oxideto the combined pyrrhotite, whereby the treatmentA of pyrrhotite is thesole source of sulfur dioxide in the system, and recovering ferricoxide. v

3. That method of roasting pyrites to produce sulfur and ferrie oxidecomprising uidizing one portion of pyrites with nitrogen-containing gasSubstantially free from oxygen at a temperature 'to drive off the labilesecond portion of pyrites in the same manner, recovering the sulfur fromsaid treatments, iiuidizing the pyrrhotite from said one portion with anoxygen-containing gas at a temperature to convert it to magnetite andproduce sulfur dioxide, treating the pyrrhotite from said second portionwith sulfur dioxide, including that from said one portion, at atemperature and with uidization to convert it to magnetite withproduction of a mixture of sulfur dioxide and sulfur vapor, condensingsulfur from said mixture and passing the residual sulfur dioxide to aheater, passing sulfur dioxide 1rom the heater to treat said one portionand another part to treat the pyrrhotite from said second portion,uniting the magnetite thus produced and uidizing it with anoxygen-containing gas to convert it to ferrie oxide, and recovering theferrie oxide.

4. That method of roasting pyrites comprising the steps of uidizingpyrites with non-oxidizing gas at a temperature to drive oiiC the labilesulfur atom and form pyrrhotite, recovering the sulfur thus produced,dividing Said pyrrhotite into two portions, fluidizing one of saidportions with sulfur dioxide at a temperature to form magnetite and amixture of sulfur dioxide and sulfur vapor, recovering sulfur from saidmixture and passing part of the sulfur dioxide to treat said one portionand another part to fiuidize the other of said portions at a temperatureto produce magnetite and a mixture of sulfur dioxide and sulfur vapor,recovering sulfur from said lastnamed mixture, combining the magnetitethus produced and uidizing it with an oxygen-containing gas at atemperature to convert it to ferrie oxide, and recovering the ferrieoxide.

5. That method of roasting pyrites comprising the steps of uidizingpyrites with non-oxidizing gas at a temperature to drive off the labilesulfur atom and form pyrrhotite, recovering the sulfur thus produced,dividing said pyrrhotite into two portions, uidizing one of saidportions With sulfur dioxide at a temperature to form magnetite and amixture of sulfur dioxide and sulfur vapor, recovering sulfur from saidmixture and passing part of the sulfur dioxide to treat said one portionand another part to uidize the other of said portions at a temperatureto produce magnetite and a mixture of sulfur dioxide and sulfur vapor,recovering sulfur from said lastnamed mixture, combining the magnetitethus produced and udizing it with an oxygen-containing gas at atemperature to convert it to ferrie oxide, and supplying said sulfurdioxide solely by returning a portion of said ferric oxide to thecombined magnetite to react with pyrrhotite with production of magnetiteand sulfur dioxide, andv recovering the ferric oxide.

6. That method of roasting pyrites comprising the steps of fiuidizingpyrites with non-oxidizing gas at a temperature to drive oi the labilesulfur atom and form pyrrhotite, recovering the sulfur thus produced,dividing said pyrrhotite into two portions, uidizing one of saidportions with sulfur dioxide at a temperature to form magnetite and amixture of sulfur dioxide and sulfur vapor, recovering sulfur from saidmixture and passing part of the sulfur dioxide to treat said one portionand another part to uidize the other of said portions at a temperatureto produce magnetite and a mixture of sulfur dioxide and sulfur vapor,recovering sulfur from said last- .nanied mixture, combining themagnetite thus produced and uidizing it with air at a temperature toconvert it to ferrie oxide and in an amount such that the oli-gas issubstantially oxygen free, passing said off-gas to iiuidize saidpyrites, and recovering the ferric oxide.

7. That method of roasting pyrites comprising the steps of uidizingpyrites with non-oxidizing gas at a temperature to drive off the labilesulfur atom and form pyrrhotite, recovering the sulfur thus produced,dividing said pyrrhotite into two portions, uidizing one of saidportions with sulfur dioxide at a temperature to form magnetite and amixture of sulfur dioxide and sulfur vapor, recovering sulfur from saidmixture and passing part of the sulfur dioxide to treat said one portionand another part to uidize the other of said portions at a temperatureto produce magnetite and a mixture of sulfur dioxide and sulfur vapor,recovering sulfur from said lastnamed mixture, combining the magnetitethus produced and uidizing it with air at a temperature to convert it toferrie oxide, said air being in an amount such that the ot-gas issubstantially oxygen free, passing said oft'- gas to uidize saidpyrites, supplying said sulfur dioxide solely by returning a portion ofsaid ferric oxide to the combined magnetite to react with pyrrhotite toform magnetite and sulfur dioxide, and recovering ferrie oxide.

References Cited in the tile of this patent UNITED STATES PATENTS1,941,592 Bacon etal Jan. 2, 1934

1. THAT METHOD OF ROASTING PYRITES TO PRODUCE SULFUR AND FERRIC OXIDECOMPRISING FLUIDIZING ONE PORTION OF PYRITES WITH NITROGEN-CONTAININGGAS SUBSTANTIALLY FREE FROM OXYGEN AT A TEMPERATURE TO DRIVE OFF THELABILE SULFUR ATOM AND FORM PYRRHOTITE, SEPARATELY FLUIDIZING A SECONDPORTION OF PYRITES IN THE SAME MANNER, RECOVERING THE SULFUR FROM SAIDTREATMENTS, FLUIDIZING THE PYRRHOTITE FROM SAID ONE PORTION WITH ANOXYGEN-CONTAINING GAS AT A TEMPERATURE TO CONVERT IT TO MAGNETITE ANDPRODUCE SULFUR DIOXIDE, FLUIDIZING THE PYRRHOTITE FROM SAID SECONDPORTION WITH SULFUR DIOXIDE, INCLUDING THAT FROM SAID ONE PORTION, AT ATEMPERATURE TO CONVERT THE PYRRHOTITE TO MAGNETITE WITH PRODUCTION OF AMIXTURE OF SULFUR DIOXIDE